In a conventional method of fastening a rotary tool, such as a grinding wheel or a cutter, to a spindle by axially pressing the rotary tool, the rotary tool is pressed axially with a fastening nut screwed on an externally threaded end part of the spindle to hold the rotary tool between a flange formed on the spindle and the fastening nut. Generally, the hand of the external thread of the spindle and the internal thread of the fastening nut is determined so that the fastening nut may be turned in a fastening direction by its own inertia at the start of rotation to maintain the fastening force of the fastening nut during rotation.
It is difficult to unfasten the fastening nut by hand when removing the rotary tool which has been fastened tighter by the increasing fastening effect of the fastening nut during operation for an extended period of time under severe conditions. A fastening device for axially fastening a tool disclosed in JP-2-502359 B incorporates a technique developed to solve such a problem.
As shown in FIGS. 14A and 14B, a prior art fastening device has a fastening nut 102 screwed on a threaded end part 101a of a spindle 101, and a fastening disk 103 axially movably fitted on the fastening nut 102 and restrained from turning. The respective holding surfaces 102a and 103a of the fastening nut 102 and the fastening disk 103 are formed so as to define a space having a V-shaped cross section. Three support members 104 having the shape of a segment and a V-shaped cross section corresponding to that of the space defined by the holding surfaces 102a and 103a are supported for radial movement in the space between the holding surfaces 102a and 103a.
Raceways 104a for balls 105 are formed in the outer side surfaces of the support members 104. An operating member 106 provided with a raceway 106a in its inner circumference is interposed between the fastening nut 102 and the fastening disk 103 and is supported by the three balls 105 which roll along the circumferential raceways 104a and 106a. Three recesses 106b are formed in the raceway 106a of the operating member 106. The turning range of the operating member 106 is defined by stoppers 107 and 108, and the operating member 106 is biased by springs 109 in the fastening direction of the fastening nut 102.
When unfastening a tool 110 fastened to the spindle 101 by the fastening device thus constructed, the operating member 106 is turned by hand in the unfastening direction of the fastening nut 102. The operating member 106 supported by the balls 105 is turned against the forces of the springs 109, and the balls 105 drop into the recesses 106b. Consequently, the support members 104 are able to move radially outward, and the fastening disk 103 is able to move axially away from the tool 110, so that the fastening nut 102 can be easily unfastened.
The fastening device of the prior art disclosed in JP-2-502359 B for axially pressing a tool to fasten the same has a complicated construction, comprises a large number of parts, is expensive, has problems in the stability of operation, operability and durability, and is capable of being applied to a limited purpose for fastening a rotary tool. The present invention has been made by solving those problems in the prior art and it is an object of the present invention to provide a fastening device having a simple construction, inexpensive, capable of stable operation, and capable of being easily fastened and unfastened by a force exerted thereon by finger tips without using any special tool. The fastening device of the present invention is applicable to fastening various stationary members as well as rotary tools.